Written and medically reviewed by Dr. Daniel Chong. Last reviewed 2026-09-10. 10 min read
The number most people have never been told
A great many people are walking around iron deficient with a blood test their doctor described as normal. Not because anyone made a mistake, but because the test that finds it is often not the test that was done.
The full blood count is the standard screen, and haemoglobin is the number it reports. The difficulty is that haemoglobin is the last thing to fall.
Iron depletes in stages. The stored iron goes first, held mostly in the liver and measured by ferritin. Then the iron in transit falls. Only after both are exhausted does haemoglobin begin to drop and anaemia appear on a routine blood count.
That leaves a long middle period, sometimes years, where someone is genuinely iron deficient, genuinely symptomatic, and entirely normal on the test they were given.
Ferritin is the number that finds it. Broadly, below about 30 micrograms per litre indicates depleted stores in most adults, and below 15 is unambiguous. The catch is that many laboratory reference ranges begin lower than that, so a result printed without a flag beside it can still represent real deficiency. The number has to be read against the person, not against the range.
What it actually feels like
Iron deficiency rarely announces itself. It is more often a gradual narrowing of what feels normal.
Fatigue that rest does not fix. The commonest presentation and the easiest to attribute to work, age or sleep.
Breathlessness on stairs or during exercise that used to be comfortable.
Hair shedding. We see this frequently, and it is one of the few genuinely correctable causes of hair loss. Our page on hair loss assessment puts the blood test before the scalp treatment for exactly this reason.
Poor concentration, sometimes described as brain fog.
Brittle nails, cold hands and feet, headaches, restless legs.
Pica, an urge to chew ice or other non-food substances, which is unusual enough that it is worth mentioning to a doctor.
None of these is specific to iron. All of them are reasons to check.
Who tends to be affected
Menstruating women, by a considerable margin. Regular monthly loss is the single most common cause, and heavy periods more so. Many women have been mildly deficient for so long that they have no recent memory of feeling otherwise.
Pregnancy and the postpartum period, where requirement rises sharply.
Anyone eating little or no red meat, including vegetarian and vegan diets, where iron is present but absorbed considerably less efficiently.
Endurance athletes, through a combination of losses and demand.
People with gastrointestinal conditions, coeliac disease, inflammatory bowel disease, or a history of gastric surgery, where absorption is the problem rather than intake.
Regular blood donors.
And one group worth naming separately: people already taking iron tablets who are not improving. That is not a reason to take more tablets. It is a reason to find out why they are not working.
Why oral iron fails for some people
Tablets are the right first answer for most people, they are inexpensive, and where they work they work well. This section is about the substantial minority for whom they do not.
Absorption is the main obstacle. Only a fraction of an oral dose is absorbed at the best of times. Inflammation reduces it further, through a signalling protein that effectively shuts the gut door to iron. Tea, coffee, calcium, antacids and certain medications reduce it further again, and most people take their tablet at breakfast alongside at least one of those.
Side effects stop people taking it. Nausea, constipation, dark stools and abdominal discomfort are common, and many patients quietly stop within a few weeks without mentioning it.
Time. Even taken perfectly, replacing depleted stores by mouth takes months, not weeks.
And ongoing losses. Where iron is still being lost faster than a tablet can replace it, the arithmetic does not work regardless of compliance.
What intravenous iron does differently
An infusion bypasses the gut entirely. The iron enters the bloodstream directly and is taken up into the body's stores, which is why a single properly dosed session can deliver what months of tablets would, without the gastrointestinal problems that stopped the tablets being taken.
Modern preparations allow a large dose in one sitting. The infusion itself typically runs over twenty to thirty minutes, with observation afterwards.
It is a medical procedure, not a wellness service. That distinction matters and we have written about it separately. It requires assessment before, monitoring during, and a doctor and resuscitation equipment present in the room rather than in the building.
On safety, honestly. Serious reactions with contemporary agents are rare, reported in fewer than one in two hundred thousand infusions. Rare is not zero, and a history of significant allergy or reactive airway disease raises the risk profile. A transient metallic taste during the infusion is common and harmless. Temporary skin staining can occur if the solution leaks at the cannula site, which is why placement and monitoring matter.
One point worth knowing because it rarely reaches patients: the available preparations are not interchangeable. They differ in how much can be given at once, and in their effect on blood phosphate, where the difference between agents is substantial rather than marginal. Which one suits you is a prescribing decision made after assessment, not a preference to be selected.
Finding low iron is the beginning of the question
This is the part that separates a clinic from a drip service, and it is the reason we will sometimes decline to infuse.
Iron does not simply disappear. If yours is low, something is causing it, and in most cases the cause is straightforward: menstrual loss, pregnancy, diet, a known gut condition. But not always.
Unexplained iron deficiency in a man, or in a woman past menopause, warrants investigation rather than replacement alone. Correcting the number without asking why can mask something that needed finding.
So the assessment asks about periods and their heaviness, diet, gut symptoms, medication including anti-inflammatories and acid suppressants, surgical history and family history. Where the picture warrants it, we investigate or refer before treating.
Replacing the iron is the easy part. Knowing whether that is the whole answer is the job.
What the assessment involves
Blood work first. Ferritin and full blood count as a minimum, with transferrin saturation, C-reactive protein and renal function where indicated. Ferritin rises with inflammation, which can make a deficient person look replete, so it is interpreted alongside an inflammatory marker rather than alone.
A history that takes time. See the section above. This is where the useful information is.
A decision about route. For many people the answer is oral iron done properly, which often means a different dose, a different timing, or alternate-day rather than daily. Intravenous is for those in whom oral has failed, is not tolerated, is unlikely to work fast enough, or where absorption is the known problem.
Dose calculated, not estimated. From body weight and haemoglobin, not from a standard bag.
And a recheck at six to eight weeks, because the point is replenished stores rather than a completed appointment. If the ferritin has not moved as expected, that itself is information.
When we will say no
Where iron is not actually low, and someone has arrived asking for an infusion because they are tired. Fatigue has many causes and iron is only one of them.
Where there is iron overload, an active infection, or a previous reaction to intravenous iron.
Generally during the first trimester of pregnancy, and in later pregnancy in coordination with your obstetric team rather than independently of it.
And where the deficiency is unexplained in someone whose profile makes that finding significant. In that situation the right next step is investigation, and we will say so even though it is not what anyone books an appointment hoping to hear.
Who assesses this
Iron assessment and infusion sits within our longevity and metabolic pathway, doctor-led throughout and following diagnostics rather than preceding them. Blood work is interpreted by a doctor, the dose is calculated rather than standardised, and the infusion is administered under medical supervision.
AOKLINIK is a registered medical clinic practising in Penang since 2013. The RM50 consultation covers the assessment that determines whether an infusion is appropriate for you at all, and it is charged whether or not you proceed.
Common questions
Interpretation depends on the laboratory and on the clinical picture, but broadly, a ferritin below about 30 micrograms per litre indicates depleted iron stores in most adults, and below 15 is unambiguous deficiency. The difficulty is that many laboratory reference ranges start lower than that, so a result reported as normal can still represent genuine deficiency. This is why the number is read alongside your symptoms rather than on its own.
Yes, and this is the most commonly missed situation. Haemoglobin is the last thing to fall. Your body depletes its stored iron first, then the iron in transit, and only then does the haemoglobin drop. Someone can be genuinely symptomatic with an entirely normal full blood count, which is why we test ferritin rather than relying on the blood count alone.
Usually one of three reasons. Absorption is poor, particularly where there is inflammation, coeliac disease or a gastric condition, or where it is taken with tea, coffee, calcium or certain medications. Side effects are common enough that many people quietly stop. Or the losses are ongoing and outpacing what a tablet can replace.
With modern preparations and proper supervision, serious reactions are rare. Severe allergic reaction is reported in fewer than one in two hundred thousand infusions with contemporary agents. That is rare and it is not zero, which is why it belongs in a clinic with a doctor present and resuscitation equipment in the room, not in a setting where an infusion is treated as a wellness service.
The infusion itself typically runs over twenty to thirty minutes, with a period of observation afterwards. Allow around an hour and a half in clinic for a first appointment including the assessment.
Ferritin rises quickly, but how you feel follows the correction of the underlying deficiency rather than the infusion itself, and that takes time. Many patients notice a change over several weeks. We recheck ferritin at around six to eight weeks to confirm the stores have actually been replenished.
Anyone whose iron is not actually low, which is why we test rather than treat symptoms. Also anyone with iron overload or a condition causing it, an active infection, a history of reaction to intravenous iron, and generally during the first trimester of pregnancy. A history of significant allergy or reactive airway disease raises the risk profile and changes how the decision is made.
No, but you do need an assessment and recent blood work. If you have ferritin and full blood count results from the last few months, bring them. If not, we test first. We do not infuse iron on the strength of symptoms alone.
This page is general information and does not replace individual assessment. Iron deficiency is a medical diagnosis requiring blood testing, and intravenous iron is a prescription medicine administered only after individual assessment by a registered medical practitioner, under medical supervision in a registered facility. It carries risks including allergic reaction. Laboratory reference ranges and thresholds vary between laboratories. Suitability and outcomes vary between individuals and no result can be guaranteed.